Dandelions make seeds without fertilisation, cloning themselves through apomixis
A dandelion clock looks like the product of sex, but many of those seeds are clones. Through apomixis, dandelions, hawkweeds, some citrus and Kentucky bluegrass form seeds without fertilising the embryo. Some even need pollen to trigger growth while taking none of its genes, a trick called pseudogamy.
Plants reproduce in two broad ways. Sexual reproduction fuses gametes and yields offspring genetically unlike either parent. Asexual reproduction involves one parent and produces copies identical to it, barring mutation, through budding, fragmentation, spores, regeneration or vegetative propagation. Botanists split asexual plant reproduction into vegetative reproduction, where a piece of the plant grows into a new individual, and agamospermy, or apomixis, which substitutes for sex and sometimes involves seeds. Some apomictic plants skip seeds altogether, producing tiny plantlets or bulbils where flowers would be.
Vegetative reproduction occurs mostly in perennials, usually via modified stems or roots and occasionally leaves. It lets plants persist from season to season and spread, forming a clonal colony whose apparent individuals, called ramets, are all genetically identical. Seen one way, this is less reproduction than an individual's survival and expansion, yet each new plant is independent in every respect except its genes.
Several organs do the work. Rhizomes are underground stems whose tips break away as new plants, as in iris, couch grass and nettles. Runners or stolons creep along the surface in strawberries, many grasses and some ferns, and can cover wide areas within a few growing seasons. Adventitious buds sprout from shallow roots or damaged stems such as tree stumps, and suckering sends up new shoots from an existing root system, typical of elms and members of the rose family like Rubus.
Cloning carries a cost. Diseases pass readily from a parent to its vegetative offspring, whereas it is unusual, though not unknown, for pathogens to travel into seeds, whether those seeds come from sexual reproduction or apomixis.
Source: Plant reproduction
